The present invention relates generally to axial piston pumps, and more particularly to a variable delivery axial piston pump with outer diameter inlet filling via a fixed angle drive plate.
The invention described in U.S. Pat. No. 6,035,828 to Anderson et al. shows a variable delivery fixed displacement pump. Anderson also discloses a fixed angle drive plate and an electronic control unit which can alter the effective fluid displacement achieved by each pumping stroke. This design has met with tremendous success and represents a substantial improvement over earlier systems, however, there remains room for improvement.
For instance, the drive plate in Anderson is mounted on frustoconical roller bearings to ensure smooth rotation. While this design achieves its intended purpose, a significant amount of engine torque is wasted in overcoming the roller bearings"" friction. In addition, frustoconical bearings are relatively expensive and subject to failure like any other moveable metallic component. It would thus be desirable to reduce the cost and the friction between the drive plate and the pump housing. In addition, refilling of the hollow piston interiors takes place by drawing fluid from the pump""s low pressure interior via an opening in the outer radius of the drive plate. Consequently, engine power used to supply the pump with hydraulic fluid is less than fully exploited, resulting in a reduction in efficiency. It would thus be desirable to employ a design which takes advantage of the hydraulic fluid inlet pressure.
The present invention is directed to overcoming one or more of the problems or disadvantages set forth above.
In one aspect, a drive plate for an axial piston pump is provided which comprises a metallic component having a centerline and a drive surface oriented at a drive angle that is different from 90 degrees relative to the centerline. The metallic component further includes a radial outer surface surrounding the centerline, and defines a fill passage that extends between the radial outer surface and the drive surface. The fill passage includes an annular groove that is defined by the radial outer surface.
In another aspect, a pump is provided which comprises a housing defining an inlet. A plurality of pistons are provided, each defining a hollow interior, and are arranged around a centerline. A rotatable drive plate is also provided and defines a fill passage extending between a radial outer surface and a drive surface. The hollow interiors of the plurality of pistons are in fluid communication with the inlet via an annular groove defined by at least one of the housing and the drive plate.
In still another aspect, a method of pumping fluid is provided which comprises the step of reciprocating a plurality of pistons at least in part by rotating a drive plate. The method also includes the step of fluidly connecting a pumping chamber of a portion of the pistons to an inlet via an annular groove that is a portion of a fill passage extending between a radial outer surface and a drive surface of the drive plate. The method also includes the step of fluidly connecting a pumping chamber of a different portion of the pistons to an outlet.